Our country has a large population, the amount of cash in circulation is huge. According to statistical data of the People's Bank of China, monetary aggregates in circulation of China reaches 6.7 trillions yuan RMB by the first quarter of 2014. Battered paper currency in circulation occupies a large proportion, it is a quite tricky problem for each bank to count, select the paper currency and discriminate a version of the paper currency. In order to improve the cleanliness degree of RMB in circulation and maintain the credibility of RMB, the People's Bank of China has developed “Selection Standard on RMB Not Suitable for Circulation”. The paper currency with an obvious fold or deformation belongs to one situation of RMB not suitable for circulation. Thus it is required to automatically determine whether a fold exists in the paper currency and whether the fold degree of the paper currency affects common circulation of the paper currency.
In the conventional method for identifying the paper currency fold, a captured image of the paper currency is processed, it is determined whether a fold exists in the paper currency through change of gray values of adjacent pixels of the captured image of the paper currency, and then it determined whether the fold degree of the paper currency affects circulation of the paper currency based on an experience value or a threshold determined by analyzing statistics of a certain amount of paper currency samples. As a contact image sensor of a paper currency capturing device has a temperature characteristic, there are differences among the gray values of the pixels of the images of the paper currency captured at different temperatures. In a case that the gray values are significantly affected by the temperature, a color cast phenomena occurs at different degrees in the captured images of the paper currency, and identification of the paper currency fold is affected. Moreover, a single statistical model has an uncertainty, which may not satisfy a requirement of an accurate identification of the paper currency fold.